Pipelines are commonly used for the transport of petroleum products, with steels as the most commonly used tubular materials for transport purposes. The pipe employed may range from four inches to over forty-eight inches in diameter, and have a minimum yield strength rating of 40,000 psi. Transported fluids may flow at velocities from 3 ft/sec to over 60 ft/sec, and may cause pressures on the pipeline to be from atmospheric pressure to over 1,500 psi. These physical demands will have an effect on the constitution of the pipeline. Moreover, the presence of water and corrosive impurities in the petroleum products such as hydrogen sulfide, carbon dioxide and organic acids, leads to corrosion of the pipeline. The problem is particularly severe when the pipelines are used to transport fluids at high flow velocities.
In the oilfield, brine, oil and gas make up the petroleum products which may travel through the pipe in separate phases or in a stable emulsion. Both conditions will be represented by the term oil-in-brine emulsion hereafter. Corrosion increases sharply as the salt content of the brine in the oil-in-brine emulsion increases to about 15% total dissolved solids. Low pH brines tend to be more corrosive. Additional factors contributing to corrosion within the pipelines concern the makeup of the transported oil, which itself may contain organic acids, paraffins, asphaltenes and aromatics. The gravity of the crude, the amount of acid gases, the salt content and composition all have an effect on corrosivity. Further, as temperature and pressure increase, they result in an increase in corrosion rate.
In order to protect the pipelines from this corrosive environment, it is now common to treat the fluids transported by these pipelines with small quantities of corrosion inhibitors. Nitrogen-containing water-soluble molecules such as imidazoline salts as disclosed in DE 2846977 and polymerized fatty acids disclosed in U.S. Pat. No. 4,197,091 are among the compounds which have been successfully employed as corrosion inhibitiors. Other classes of corrosion inhibitors commonly used in petroleum production include amides, amines, quaternary ammonium salts, nitrogen-containing heterocycles, and sulfur-containing compounds. Though several classes of corrosion inhibitors are known, it would be of great benefit to the art to increase the activity of corrosion inhibition additives.
Another factor which affects the transport of petroleum products, is friction produced by turbulent flow as the petroleum products travel through the pipeline at high velocities. For example, in Prudhoe Bay, Ak., the produced fluids travel inside 24 inch (61 cm) diameter multiphase pipelines from approximately 25 ft/sec to 50+ ft/sec depending upon production. The turbulence produced as the solutions are pumped through the pipe under pressure results in the production of friction. As a remedy, friction reducing agents such as polymeric materials can be added to the stream to prevent consequent energy loss in the flow of the fluid as it travels throught the pipeline. A good friction reducer will cause a large decrease in friction at small concentrations, will be inexpensive, and will have high shear, temperature and pressure stability.
Water-soluble polymers such as polyacrylamide are known for reducing pipeline friction as disclosed in U.S. Pat. No. 3,254,719, the specification of which is hereinafter incorporated by reference. Polyacrylamide has also been combined with dispersing agents, as disclosed in U.S. Pat. No. 3,542,044 and with other co-polymers as disclosed in U.S. Pat. No. 4,152,274. Generally, the polymers are injected continuously into the pipeline.
French et al., U.S. Pat. No. 5,027,901, discloses a method of inhibiting corrosion in an oil well comprises introducing into the well a pourable emulsion comprising 5-50% of a continuous oil phase containing a corrosion inhibiting compound. This technique was specifically designed for the unique problems presented by a vertical pumping action, and thus does not address the problems associated with the horizontal flow across a pipeline improved by the method disclosed herein. Moreover, the polymers of this invention are not taught by this reference.
Smith et al., U.S. Pat. No. 3,102,548 describes a process wherein polyacrylamide is added to an aqueous fluid which is pumped under turbulent flow conditions. There is no teaching or suggestion that a polymer which enhances the flow of aqueous fluids will also be effective to enhance anti-corrosive capabilities of corrosion inhibitors in oil-in-brine emulsions of crude oil. Moreover, a treatment agent which enhances fluid flow would ordinarily be thought to increase corrosion, not decrease it.
Martin et al., U.S. Pat. No. 4,339,349 discloses compositions useful as corrosion inhibitors. Methods for the enhancement of these activities in pipelines are not described therein.
Acrylamide polymers, as the term is used herein, includes polymers consisting entirely of acrylamide units, which may be partially hydrolyzed to acrylic acid units. The term acrylic acid units encompasses the various salts such as the sodium or potassium salt form of the acrylic acid. This hydrolysis of amide groups to carboxylic acid groups may be conducted using alkaline materials such as sodium hydroxide, ammonium hydroxide, soda ash, potassium hydroxide, or quaternary ammonium hydroxide. Optimum partial hydrolysis of polyacrylamide for operation as a friction loss reducer is described in U.S. Pat. No. 3,254,719 as 20 to 40 percent hydrolysis of available amide groups.
Polyacrylamide may be synthesized as one of three forms: solid, solution or emulsion. Dry polymer may be obtained by solution polymerization with a high concentration of monomer. The resultant gel can be ground and dried to obtain polyacrylamide in a powdered form. Solution polymerization with up to 15% monomer results in an aqueous solution of polyacrylamide. Lastly, polyacrylamide can be made in the form of an aqueous water-in-oil emulsion. The emulsion is formed by utilizing a water-in-oil emulsifying agent. To this monomer is added a free radical-type polymerization catalyst and then heat is applied under free radical-forming conditions to form water-soluble polymer lattices. The polymer lattices may be unstable, and therefore must be treated with additional emulsifiers. The preparation of these emulsions is described in U.S. Pat. No. 3,284,393. Subsequently, the emulsions may be inverted to produce aqueous solutions.
Another class of water-soluble polymers useful in this invention are water-soluble cationic polymers dispersed in aqueous solutions of inorganic salts. The inorganic salt may be a sulfate, a chloride or a phosphate, but is preferably ammonium sulfate. Cationic monomers such as dimethylaminoethyl acrylate, dimethylaminoethyl methyacrylate methyl chloride quaternary salt and dimethylaminoethyl methacrylate benzyl chloride quaternary salt may be used to form dispersed homopolymers. Alternatively the cationic monomers described above can be co-polymerized with acrylamide, or ter-polymers may be formed by combinations of cationic monomers with acrylamide.
It is therefore an object of the invention to provide the art a superior method for enhancing the effect of corrosion inhibitors in pipelines transporting oil-in-brine emulsions.